How do barnacles stick to the undersides of vessels, to other sea life, to each other, and to pretty much anything they come in contact with? They secrete a fast-curing cement that is among the most powerful natural glues known, with a tensile strength of 5,000 pounds per square inch and an adhesive strength of 22-60 pounds per square inch. The glue is so strong that researchers are trying to figure out how it can be used commercially.